Utility companies in urban areas frequently use underground substations. Each substation resides in a “vault” and includes one or more transformers. Some vaults are small and consist of only a single transformer, while other vaults are large and consist of several transformers. The substations also typically include wires, power panels, lights, receptacles and other components normally found in an electrical utility system.
Within urban areas, substations are connected to form a subterranean electrical power grid. For example, the City of Memphis, operating through Memphis Light, Gas & Water (or “MLG&W”) uses a 115 kV underground “pipeline” that runs through parts of the city, particularly downtown, where surface utilities are impractical and unsightly. The utility's 115 kV pipeline system consists of 40 manholes for accessing the individual substations. The manholes generally reside at sidewalk or street level.
Because the vaults are underground, they are subject to water invasion when it rains. The presence of water in the vault creates a number of problems. For example, a wet floor can create a safety hazard to maintenance personnel. Also, the presence of water creates an environment of high humidity. This, in turn, contributes to rusting and pitting of the metal components in the substations. More seriously, the presence of water creates a potential for electrical shock and electrical outage of the system.
In order to reduce the presence of water, each vault is covered by a manhole cover or grate. In addition, each vault is commonly equipped with a sump pump. The pumps are controlled by a dielectric sump pump control mechanism. Each mechanism includes a first probe at ground level, and a second probe just above ground level. The control mechanism takes advantage of the conductivity of the water, and uses the water to complete the circuit formed by the probes and the pump. When the water contacts each of the probes, the pump is electrically activated. Then when the sump pump is activated, water is pumped out of the vault. Typically, the water is simply pumped into the street.
A problem arises when water invades the vault at a rate faster than the pump can remove it. When the vault floods, the controls that operate the sump pump are exposed to water. Conventional sump pump controls are normally damaged beyond repair once the vault is flooded with water. Of course, the presence of a high level of water also may damage the power panels, lights, receptacles, wiring, transformers, and protectors that make up the substation.
Another problem arises when oil leaks into a substation. Oil may be present when a transformer or other item of equipment begins to leak or lose containment of an insulating and/or heat-dissipating fluid. A sump pump that begins to pump oil will simply pump the oil into the street, creating an environmentally undesirable circumstance.
In light of the above problems and others, a need exists for an improved sump pump control. A need further exists for a sump pump control that is able to operate when a vault for a substation becomes flooded without being exposed to liquids. Still further, a need exists for a sump pump control that shuts off before oil is substantially pumped out of the vault.